Because there's something just so gosh-darn irresistible about murderous barbers and human flesh-filled meat pies...
The above clip is from the 1982 production of Sweeney Todd: The Demon Barber of Fleet Street, the 1979 Tony Award-winning musical by Stephen Sondheim (music and lyrics) and Hugh Wheeler (book).
The character of Sweeney Todd first appeared in The String of Pearls: A Romance, a nineteenth century penny dreadful. Originally, Todd was a barber who murdered his customers for their money (his preferred method was by slitting their throats with a straight razor). In 1973 playwright Christopher Bond gave Todd a tragic back story and turned him into a somewhat sympathetic character motivated by revenge rather than greed. The Sondheim musical is based upon Bond's play.
Todd's accomplice, Mrs. Lovett, the pie shop proprietress who uses her pies to dispose of his victims (said pies being very popular with her unsuspecting customers) was there from the beginning. Later versions have her develop a crush on the barber, but she remains pretty much the same.
Since his first appearance over 160 years ago, the Demon Barber has become a multi-media phenomenon appearing on stage (drama and musical), film (at least 5 versions including 2 silents), television (3 separate productions), radio (in a 1947 CBC dramatization and as a character in an episode of The New Adventures of Sherlock Holmes), and dance (in a 1959 performance by The Royal Ballet Company). He even appeared in the pages of a comic book (by Neil Gaiman).
The most recent version is Tim Burton's 2007 film adaptation of the Sondheim musical starring Johnny Depp and Helena Bonham Carter. I finally saw this over the weekend and enjoyed it more than I expected; I'd seen the original Broadway production back when the world was young and was a bit hesitant. I had no idea that Depp could sing - and he has a surprisingly powerful voice (is there anything he can't do?). At times it over-shadowed Carter's softer voice, but both were excellent in their roles. My main complaint was that Burton removed my favorite number, The Ballad of Sweeney Todd.